Process for synthesis of molybdenum sulfide-based catalysts

Abstract

A process for preparing a molybdenum sulfide-based catalyst comprises drying a precipitated molybdenum sulfide-based catalyst precursor, for example, a wet filter cake, such that a particulate catalyst precursor, containing from 12 to 15 percent by weight water, is formed. The particulate catalyst precursor is desirably in the form of free-flowing particles. The particulate catalyst precursor is then auto-reduced. A rotary furnace that subjects the catalyst precursor to at least two zones having distinct temperatures may be conveniently used for drying, auto-reduction, or both. The staged drying and auto-reduction steps reduce the tendency of the precursor to self-heat, which is undesirable because it reduces both the activity and selectivity of the final catalyst.

What is claimed is: 
     
       1. A process for preparing a catalyst, comprising
 drying a precipitated catalyst precursor containing at least molybdenum and sulfur such that it contains from 12 to 15 weight percent water; 
 simultaneously with or subsequently to drying, accomplishing passivation of the precipitated catalyst precursor by exposing it to air, an inert atmosphere, or a combination thereof under conditions suitable to form a passivated particulate catalyst precursor, 
 passivation being defined to mean that the particulate catalyst precursor does not self-heat to more than 100° C. if exposed to air; and then 
 thermally auto-reducing the passivated particulate catalyst precursor at a temperature ranging from 350° C. to 550° C. to form a catalyst. 
 
     
     
       2. The process of  claim 1  wherein the precipitated catalyst precursor is prepared from a reaction product of cobalt acetate, ammonium heptamolybdate and ammonium sulfide; or of ammonium tetrathiomolybdate and cobalt acetate; or of ammonium heptamolybdate and ammonium sulfide. 
     
     
       3. The process of  claim 1  wherein the drying is carried out by either pressure filtration followed by vacuum drying, or by preparing a suspension of the precipitated catalyst precursor and then spray-drying the suspension. 
     
     
       4. The process of  claim 1  wherein the drying is accomplished under vacuum and includes exposing the precipitated catalyst precursor to air, with or without added nitrogen, such that the precipitated catalyst precursor is simultaneously passivated. 
     
     
       5. The process of  claim 1  wherein the passivated particulate catalyst precursor is vacuum dried and in the form of free-flowing particles having an average size greater than U.S 40 mesh (0.400 mm). 
     
     
       6. The process of  claim 1  wherein the drying, passivation and auto-reduction are carried out in a rotary furnace. 
     
     
       7. The process of  claim 6  wherein the rotary furnace is fitted with a screw for moving the precipitated catalyst precursor into and through the furnace. 
     
     
       8. The process of  claim 7  wherein the rotary furnace has at least two distinct temperature zones, including a first temperature zone from 150° C. to 400° C.; and a second temperature zone from 450° C. to 550° C. 
     
     
       9. The process of  claim 7  wherein the rotary furnace has at least three distinct temperature zones, including a first temperature zone from 150° C. to 250° C., a second temperature zone from 300° C. to 400° C., and a third temperature zone from 450° C. to 550° C.